1. Field of the Invention
The present invention relates to a liquid-jet head which ejects liquids and a liquid-jet apparatus, and more particularly relates to an ink-jet recording head which ejects ink droplets and an ink-jet recording apparatus.
2. Description of the Related Art
In an ink-jet recording head, a part of pressure generating chambers communicating with nozzle orifices is formed of a vibration plate, this vibration plate is deformed by piezoelectric elements, and ink in the pressure generating chambers is pressurized to eject ink droplets from the nozzle orifices. There are two types of ink-jet recording heads which have been put to practical use, which include: one using a piezoelectric actuator of a longitudinal vibration mode, which extends and contracts in an axial direction of a piezoelectric element; and one using a piezoelectric actuator of a flexure vibration mode.
As the latter ink-jet recording head using the actuator of the flexure vibration mode, for example, there has been known one formed as described below. Specifically, a uniform piezoelectric material layer is formed on the entire surface of a vibration plate by use of a deposition technology. Thereafter, the piezoelectric material layer is cut into a shape corresponding to pressure generating chambers by use of a lithography method. Thus, piezoelectric elements are formed so as to be independent for each of the pressure generating chambers.
Here, in such an ink-jet recording head in which piezoelectric elements are densely arranged, one electrode (a common electrode) of each of the piezoelectric elements is provided so as to be shared by a plurality of the piezoelectric elements. Thus, if a number of the piezoelectric elements are simultaneously driven to eject a number of ink droplets at a time, a voltage drops and a displacement amount of the piezoelectric element becomes unstable. Consequently, there arises a problem of a variation in an ink ejecting property.
Accordingly, there has been proposed an ink-jet recording head which includes: a common lead electrode drawn out to outside of a region facing the pressure generating chambers from a portion of the common electrode except for an end in an arrangement direction of the pressure generating chambers; and a resistance reduction portion including a connection wiring formed of a bonding wire (for example, see Japanese Patent Laid-Open No. 2004-1366 (FIGS. 1 and 2)). The ink-jet recording head described above can prevent the variation in the ink ejecting property due to a voltage drop by allowing the resistance reduction portion to lower a resistance-value of the common electrode when a voltage is applied to the piezoelectric elements.
However, in the ink-jet recording head including the common lead electrode and the resistance reduction portion as described above, the common electrode and the common lead electrode are different members. Thus, a manufacturing error occurs when the common lead electrode connected to the common electrode is formed by use of the deposition technology. For example, due to a shift of a mask or etching conditions, there occurs a slight variation in dimensions such as a width of the common lead electrode or a slight shift of a formation position of the common lead electrode. Thus, the common lead electrode is protruded into the region facing the pressure generating chambers from compartment walls on both sides in a direction perpendicular to the arrangement direction of the pressure generating chambers. As a result, there arises a problem that rigidity of the vibration plate is partially enhanced to cause the variation in the ink ejecting property.
Moreover, there has been known an ink-jet recording head including a common lead electrode which is drawn out to outside of a region facing pressure generating chambers from a common electrode (for example, see Japanese Patent Laid-Open No. 2003-127358 (FIG. 3)). In the ink-jet recording head described above, the common electrode and the common lead electrode are formed to have the same pattern. Thus, it is possible to solve the problem that the common lead electrode is protruded into the region facing the pressure generating chambers to cause the variation in the ink ejecting property in the case as described above where the common electrode and the common lead electrode are separately formed.
However, the ink-jet recording head having the structure as described above has a problem that it is impossible to sufficiently prevent a voltage drop which occurs when a plurality of piezoelectric elements are simultaneously driven. To be more specific, a thickness of the common electrode may be increased to prevent the voltage drop. However, since the common electrode generally forms a portion of the vibration plate, an amount of deformation of the vibration plate due to driving of the piezoelectric elements is reduced if the thickness of the common electrode is increased. Thus, it is required to form the common electrode so as to be relatively thin. On the other hand, if the thickness of the common electrode is reduced, a resistance value is increased. Thus, there is an inconsistency that the problem of the variation in the ink ejecting property due to the voltage drop is likely to arise. Therefore, in the above-described ink-jet recording, head having the structure in which the common electrode and the common lead electrode are formed to have the same pattern, the thickness of the common lead electrode as well as that of the common electrode are reduced to cause the voltage drop. Thus, there arises the problem of the variation in the ink ejecting property. Note that, needless to say, the problem as described above similarly exists not only in the ink-jet recording head which ejects ink droplets but also in other liquid-jet heads which eject liquids other than the ink droplets.